Ionization, heating and stabilization by currents along a poloidal magnetic field

The ionization and heating effects of induced low frequency poloidal currents in the internal ring device F IV A have been studied. The start-up process is more efficient and works at lower filling pressures than without poloidal currents. The plasma temperature is increased due to ohmic heating. Rotating plasmas with a density of 1.5x1021 m-3 were obtained for a filling pressure of 6 m Torr. Fluctuations are stabilized already at low power poloidal currents. The stabilizing effect seems to be related to the applied toroidal magnetic field rather than the induced poloidal current. At the lowest filling pressures (0.2 m Torr) a nonrotating plasma, sustained only by the poloidal current, with a density of 1.5x1020 m-3 and a temperature of 7 eV was produced. At this low density, the plasma is permeable to neutral gas, as opposed to the impermeable plasmas in the earlier experiments with this device. (orig.)